I reckon it's just a difference of how you'd define gambling is? In general I don't think sports betting is gambling, hence why I call it a bet. It can BE a gamble, but it doesn't have to be one. What your uncle did was exactly that, and the same thing could be done in trading imo. Gambling on the other hand? I define that as relying completely on luck, gut, or whatever the hell you want to describe it with. Like full on ofc, imo even betting has that bit of gut in part of it but it's never really used as a reference alone, unlike gambling.
You call sports betting a bet, therefore it is actually gambling. But there is also betting word next to sports, making it an obvious gambling. Maybe you think because it involves a skill or strategy but that is already a part of gambling or we can say another category of it. Trading is trading, but gambling word can also be used here, only because there is also a stake money and not really because we do it the random way like what typical gambling game goes.
trading and investing would definitely be different. I'd probably recommend for people who have a 9-5 to just invest than trade.
The difference is that trading is usually seen as active, while investing is passive but I think there are also bots in trading which can make it a passive activity, so it could still fit for a busy person.